Japanese Patent No. 4956409 discloses an LED lighting fixture provided with a light source unit, which is constituted by an LED, and a switching power source.
The switching power source of the LED lighting fixture described in Japanese Patent No. 4956409 is configured to turn on the light source unit. The switching power source is provided with a series circuit of a first switching element and a second switching element, and a series resonance circuit of a primary winding of an output transformer, a capacitor, and an inductor. The switching power source is also provided with a first control circuit, a second control circuit, a secondary winding of the output transformer, a full-wave rectification circuit, and a smoothing capacitor. The first control circuit and second control circuit control the operation of the first switching element and second switching element, respectively. The light source unit is electrically connected between the terminals of the smoothing capacitor.
The switching power source of the LED lighting fixture described in Japanese Patent No. 4956409 is a so-called composite resonance converter. In such a switching power source, the resonance frequency of the series resonance circuit can change depending on the load state of the light source unit electrically connected between the terminals of the smoothing capacitor, and a surge current can flow therein.